Not Applicable
Not Applicable
1. Field of the Invention
This invention relates to disk drive suspensions, and more particularly to wireless suspensions in which the flexure comprises a laminate of plastic film, trace conductors, and a metal layer. In a specific aspect, the invention relates to improvements in the design and manufacture of suspension flexures to have capacitance and thus impedance values controlled separately for each trace and each pair of traces to have constant values throughout their lengths, as desired, and the same or different absolute impedance values for optimizing read and write circuit pairs, and to accommodate mechanical limitations of the flexure design, as needed for optimum flexure performance.
The invention achieves control of impedance by increasing or decreasing capacitance (to correspondingly decrease or increase impedance) of each conductive trace of a pair or pair of conductive traces through modification of trace width, and/or spacing from adjacent traces, or by changes in effective length by varying the length of a trace between defined places on the flexure, while not altering the distance between those defined places.
2. Description of the Related Art
Existing trace flexure designs have layouts that feature conductive trace paths generally as straight as possible, with any change in path direction being curved with as large as possible a radius. Generally, with multiple conductive traces routed side by side, the spacing between the traces will be at least locally uniform, that is, in any given portion of the trace flexure, the spacing between adjacent conductive traces and the trace width will not vary much. If, however, the traces after being routed alongside each other go to different destinations on the layout, such as occurs when the traces are divided to reach both sides of a slider along the outriggers.
A currently typical spacing for 0.0016 inch wide and 5 to 20 micron thick conductive traces in a wireless flexure is a 40 micron (1 micron equals 1 micrometer equals 40 micro inches) space laterally between adjacent traces. The traces thickness is determined by the flexure laminate, and is assumed to be fixed by the laminate supplier for purposes of this invention.
This width and spacing combination results in a characteristic impedance referred to as Z0, for the device and for each pair of conductive traces considered. Presently used trace flexures have a characteristic impedance of 30 or so ohms.
The putative xe2x80x9ccharacteristic impedancexe2x80x9d is not found at all points along the trace or pair of traces. Rather many variations from that impedance are found. This occurs, for example, in a disk drive suspension flexure because Z0 changes with differences in trace cross section or trace spacing arising from diverging trace pairs, and changes in routing and bends in traces around mechanical features of the flexure, such as tooling holes or weld points. It is, however, desirable that the flexure have a Z0 that is constant along the length of the traces and trace pairs throughout the flexure, and in the case of read-write circuits, constant at about 110 ohms for the write lines and at about 60 ohms for the read lines.
As the operating frequency of the disk drive increases, the importance of adhering to the constant and correct impedance becomes ever more important. Any change in impedance Z0 causes a reflection of the signal being sent along that path; the reflection represents wasted signal and an increase in noise. Both wasted signal (lost signal strength) and increased noise effectively decrease the signal to noise ratio (SNR) and thus decrease this important measure of the quality of an electronic device.
Historically, trace flexure layouts have to the good had generally large radius curves, but also uniform trace widths and spacing, all in accordance with the design rules of printed circuit boards (PCBs), which is the preceding technology to flex circuits and wireless flexures. But, PCBs were a different animal from flexures since there device placement was at the whim of the PCB designer, and mechanical constraints, so important in flexures, were not really a factor. The PCB designer could place the devices to be connected anywhere he wanted to, constant width and spacing of conductors was a design that was both correct and easy.
In making this invention it has been recognized that the simple default design taken from PCB technology does not apply to the very different case of trace flexures in which the end points of the traces are immutably fixed by exigencies of disk drive suspension technology, and their intermediate lengths are necessarily detoured around fixed obstacles implicated in suspension design, such as tooling holes and weld points.
Time Domain Reflectometry (TDR) analysis computes Z0 as a function of time as the energy passes down the trace length. TDR shows that the Z0 for an apparently uniform trace varies dramatically along the length of the trace in previously known flexure design, and even the nominal value of Z0 value about which the variation takes place is less than specifications require.
It is, accordingly, an object of this invention to provide a wireless flexure for a disk drive suspension having a constant characteristic impedance Z0 over the length of the flexure traces regardless of the presence of mechanical obstacles, curves in layout, or other factors that have caused unwanted variations in impedance along and between conductive traces and trace pairs in the flexures. It is another object to provide an improved flexure design in which the conductive traces are customized along their length to meet situations that might limit the constancy of the impedance of the trace. It is a still further object to vary locally the width and spacing of conductive traces to offset locally unwanted variations and lack of constancy in impedance imposed by the flexure design or application. Yet another object is to increase the effective length of one or more traces to increase capacitance relative to one or more adjacent traces and thus limit inversely changes in impedance constancy. It is yet another object to vary the length and configuration of one or more traces relative to another trace or traces between fixed points to change to a desired value the impedance of the one relative to the other, e.g. to increase the impedance of a write line over that of an adjacent read line.
These and other objects of the invention to become apparent hereinafter are realized in a controlled impedance trace flexure for a disk drive suspension, the trace flexure comprising a laminate of a metal layer, an insulative film layer and one or more pairs of conductive traces comprising paired trace members that extend together differentially in a pattern between two fixed points such that there tend to be unwanted local variations in the respective impedances of the paired members over their extent and therefore a lack of constancy in conductive trace impedances, the paired members being locally modified in their relative spacing, length and/or width in capacitance-varying relation sufficiently to offset the impedance variations, whereby the paired members are controlled to a constant impedance.
In this and like embodiments, typically, the paired members at a predetermined locus tend to unwanted variations in their respective impedances, and the paired members are locally differentiated in width at the predetermined locus to locally vary their capacitance against the impedance variations, or the paired members are locally differently spaced at the predetermined locus to locally vary their capacitance against the impedance variations.
Alternatively, the paired members are made locally of different effective lengths within the predetermined locus to locally vary their capacitance against the unwanted impedance variations.
In a further embodiment, the invention provides a controlled impedance trace flexure for a disk drive suspension, the trace flexure comprising a laminate of a metal layer, an insulative film layer and one or more pairs of conductive traces comprising paired trace members that extend together over a predetermined distance between two fixed points and in which there tends to be at a given locus an unwanted local variation in the impedances of the respective paired members, one of the paired members being reversely turned within the given locus to increase its effective length relative to the other paired member in capacitance-increasing relation sufficiently to make uniform the impedance of the one conductive trace with the other conductive trace, whereby the paired members are kept at a uniform impedance within the locus.
In this and like embodiments, typically, the one paired member is sinuous within the locus and has a predetermined period from peak to peak, the predetermined period being smaller than the frequency of the signals carried by the one paired member, e.g., the signal frequency is about 1 GHz, and the paired member period is less than about 1 inch.
In a further embodiment, the invention provides a controlled impedance trace flexure for a disk drive suspension, the trace flexure comprising a laminate of a metal layer, an insulative film layer and one or more pairs of conductive traces comprising paired trace members that extend together over a predetermined distance between two fixed points and in which there tends to be an unwanted variation between the total impedances of the respective paired members, one of the paired members being reversely turned within the predetermined distance to increase its effective length relative to the other paired member in capacitance-increasing relation sufficiently to make uniform the impedance of the one conductive trace with the other conductive trace, whereby the paired members are kept at a uniform impedance.
In this and like embodiments, the one paired member is sinuous and has a predetermined period from peak to peak, the predetermined period being smaller than the frequency of the signals carried by the one paired member, e.g., the signal frequency is about 1 GHz, and the paired member period is less than about 1 inch.
In a further embodiment, the invention provides a controlled impedance trace flexure having two or more pairs of conductive traces comprising members that extend together over a predetermined distance between two fixed points, one pair of conductive trace members being reversely turned within the predetermined distance to increase its effective length relative to the other pair in capacitance-increasing relation relative to the other pair, whereby the one pair has a relatively higher impedance desired in a write circuit and the other pair has a relatively lower impedance desired in a read circuit.
In this and like embodiments, the one pair has an impedance of about 110 ohms, and the other pair has an impedance of about 60 ohms.
In addition, there can be provided in this and like embodiments, a further conductive trace disposed between the pairs of conductive traces, the further conductive trace being connected to electrical ground, whereby one the pair is electrically isolated from the other pair.
In yet another embodiment, the invention provides a controlled impedance trace flexure for a disk drive suspension having two or more pairs of conductive traces each comprising paired members that extend together differentially in a pattern over a predetermined distance between two fixed points such that there tend to be unwanted local variations in the respective impedances of the paired members over their extent, the paired members being locally modified in their length through a sinuous shaping of the members within the predetermined distance sufficiently to offset the impedance variations, whereby the paired members of the pair of conductive traces are controlled to a constant impedance with each other.
In this and like embodiments, typically, the one paired member is sinuous within the locus and has a predetermined period from peak to peak, the predetermined period being smaller than the frequency of the signals carried by the one paired member, the signal frequency being about 1 GHz, and the paired member period being less than about 1 inch, and there optionally being a further conductive trace disposed between the pairs of conductive traces, the further conductive trace being connected to electrical ground, whereby one the pair is electrically isolated from the other pair.
In a still further embodiment, the invention provides a controlled impedance trace flexure for a disk drive suspension, the trace flexure comprising a laminate of a metal layer, an insulative film layer and two or more pairs of conductive traces each comprising paired members that extend together over a predetermined distance between two fixed points, the pairs of conductive traces being differentially sinuous to have different effective lengths over the predetermined distance, whereby the conductive trace pairs have different impedances from one another.
In this and like embodiments, typically, each paired member within the pairs is parallel with the other member in the pair, each sinuous pair has a predetermined period from peak to peak, the predetermined period being smaller than the frequency of the signals carried by the one pairs, and typically a signal frequency of about 1 GHz, and a period of the pairs that is less than about 1 inch.
Additionally, there can be provided a further conductive trace disposed between the pairs of conductive traces, the further conductive trace being connected to electrical ground, whereby one pair is electrically isolated from the other pair.
In its method aspects, the invention provides a method of controlling impedance in a conductive trace flexure comprising a laminate of a metal layer, an insulative film layer and one or more pairs of conductive traces that are differentially routed over their lengths, including varying the width, spacing, and/or effective length of one of the conductive traces relative to the other conductive trace until the desired impedance is achieved.
A further invention method includes controlling impedance in a conductive trace flexure comprising a laminate of a metal layer, an insulative film layer and pairs of generally parallel, spaced conductive traces that are to have different impedances over their lengths, by making the higher impedance trace sinuous over at least a portion of its length to increase its effective length and its impedance thereby.
A further invention method includes controlling impedance in a conductive trace flexure comprising a laminate of a metal layer, an insulative film layer and multiple pairs of generally parallel, spaced conductive traces in which certain pairs are to have higher impedances over their lengths, by making the higher impedance pairs sinuous over at least a portion of their lengths to increase their effective length and make their impedance higher thereby.